1. Field of the Invention
This invention relates to a method and apparatus for determining an amount of coal tar that can be displaced from a given type of soil for a range of depths of the soil. More particularly, the method and apparatus of the present invention relate to development of a relationship between the concentration of coal tar in the soil and the pressure required to displace the coal tar from the soil.
2. Description of the Related Art
Manufactured gas plants (MGPs) were typically built adjacent to streams, rivers and estuaries to supply towns with an energy source in the 1800's and continued operations until the 1960s when a network of gas pipelines was built across the country. Many MGPs were abandoned or demolished and left behind a large amount of waste and contamination that now pose a potential environmental problem. A byproduct of the gasification process was “coal tar,” which is a mixture of polycyclic hydrocarbons (PAHs) and monocyclic hydrocarbons (MAHs).
The environmental concern over the presence of coal tar as a non-aqueous phase liquid (NAPL) in the subsurface of MGP sites is a subject of interest to both regulators and the companies they regulate. The concern is centered over whether the NAPL is trapped or can be displaced from the soil into a water source. If the NAPL can be displaced from within the soil, it may flow vertically through an aquifer or laterally down sloping fine-grained stratigraphic units and either directly into a water source or indirectly into a water source by providing an additional pressure that can displace the otherwise trapped NAPL.
The types and quantities of waste discharged from MGP plants that introduced coal tar into the environment are highly varied. Coal tars are complex mixtures of over 10,000 organic compounds of varying molecular weight, functional groups and characteristics, and less than 40% of these individual compounds can be quantified using common organic chemistry techniques because of the presence of pitch. See Lee, et al. Env. Sci. and Tech. 26:2110-2115 (1992). The pitch fraction of coal tar is significant in that many components within pitch are considered relatively insoluble but still enter water to the extent of their solubility.
State regulations have presented challenges to field personnel who must quickly, consistently and accurately identify, record and characterize coal tar within a test site. The most important concern is whether a coal tar is trapped or can be displaced from a given type of soil. There is little information in the literature regarding the point at which coal tar becomes trapped in a soil. Furthermore, there is no method or system that would provide one of skill in the art with a way of determining whether coal tar is trapped or can be displaced from a given type of soil from a variety of locations within a site. Accordingly, those of skill in the art would benefit from a method or system for the determination of the amount of coal tar that can enter, and subsequently be displaced from, a given type of soil for a range of depths of the soil, and verification of the pressure at which coal tar can be displaced from the given type of soil.